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121.
Femtosecond photoelectron spectroscopy (FPES) is used to monitor the dynamics associated with the excitation of the charge-transfer-to-solvent (CTTS) precursor states in I-(NH3)n = 4-15 clusters. The FPE spectra imply that the weakly bound excess electron in the excited state undergoes partial solvation via solvent rearrangement on a time scale of 0.5-2 ps, and this partially solvated state decays by electron emission on a 10-50 ps time scale. Both the extent of solvation and the lifetimes increase gradually with cluster size, in contrast to the more abrupt size-dependent effects previously observed in I-(H2O)n clusters. 相似文献
122.
Davis FA Nolt MB Wu Y Prasad KR Li D Yang B Bowen K Lee SH Eardley JH 《The Journal of organic chemistry》2005,70(6):2184-2190
[reaction: see text] Diverse organometallic reagents readily add to enantiopure N-sulfinyl beta-amino Weinreb amides providing the corresponding, stable, N-sulfinyl beta-amino carbonyl compounds in good to excellent yields. This new methodology represents a general solution to the problem of beta-amino carbonyl syntheses, which are important chiral building blocks and constituents of natural products. N-Sulfinyl beta-amino Weinreb amides are prepared by reaction of the potassium enolate of N-methoxy N-methylacetamide with sulfinimines (N-sulfinyl imines) or lithium N,O-dimethylhydroxylamine with N-sulfinyl beta-amino esters. 相似文献
123.
Excess molar volumes at 25°C, are reported for the systems isoPrOEtOH + water and isoBuOEtOH + water across their entire composition ranges. These data have been compared to those for their normal alkyl analogs in order to assess the effects of both - and β-chain branching.
The results are discussed in terms of the relative abilities of the amphiphiles to form structured aggregates. 相似文献
124.
[reaction: see text] N-Sulfinyl beta-amino Weinreb amides are prepared by condensation of sulfinimines with the potassium enolate of N-methoxy-N-methylacetamide. These new chiral building blocks are useful for the asymmetric synthesis of beta-amino carbonyl compounds, as illustrated here by the concise enantioselective syntheses of sedum alkaloids (+)-sedridine and (-)-allosedridine. 相似文献
125.
[reaction: see text] N-Sulfinyl alpha-amino 1,3-dithioketals are prepared in high de and good yield by treating sulfinimines with lithio-1,3-dithianes. Selective removal of the N-sulfinyl or the thioketal groups affords stable alpha-amino 1,3-dithioketals and N-sulfinyl alpha-amino ketones, respectively. This new sulfinimine-derived chiral building block is employed in the asymmetric synthesis of polyoxypeptin amino acid (2S,3R)-(-)-3-hydroxy-3-methylproline. 相似文献
126.
Ritleng V Yandulov DV Weare WW Schrock RR Hock AS Davis WM 《Journal of the American Chemical Society》2004,126(19):6150-6163
Three new tetramines, (ArNHCH(2)CH(2))(3)N, have been synthesized in which Ar = 3,5-(2,4,6-t-Bu(3)C(6)H(2))(2)C(6)H(3) (H(3)[HTBTN(3)N]), 3,5-(2,4,6-Me(3)C(6)H(2))(2)C(6)H(3) (H(3)[HMTN(3)N]), or 4-Br-3,5-(2,4,6-i-Pr(3)C(6)H(2))(2)C(6)H(2) (H(3)[pBrHIPTN(3)N]). The diarylated tetramine, [3,5-(2,4,6-t-Bu(3)C(6)H(2))(2)C(6)H(3)NHCH(2)CH(2)](2)NCH(2)CH(2)NH(2), has also been isolated, and the "hybrid" tetramine [3,5-(2,4,6-t-Bu(3)C(6)H(2))(2)C(6)H(3)NHCH(2)CH(2)](2)NCH(2)CH(2)NH(4-t-BuC(6)H(4)) has been prepared from it. Monochloride complexes, [(TerNCH(2)CH(2))(3)N]MoCl, have been prepared, as well as a selection of intermediates that would be expected in a catalytic dinitrogen reduction such as [(TerNCH(2)CH(2))(3)N]Mo[triple bond]N and [[(TerNCH(2)CH(2))(3)N]Mo(NH(3))][BAr'(4)] (Ter = HTBT, HMT, or pBrHIPT and Ar' = 3,5-(CF(3))(2)C(6)H(3))). Intermediates that contain the new terphenyl-substituted ligands are then evaluated for their efficiency for the catalytic reduction of dinitrogen under conditions where analogous [HIPTN(3)N]Mo species give four turnovers to ammonia under "standard" conditions with an efficiency of approximately 65%. Only [pBrHIPTN(3)N]Mo compounds are efficient catalysts for dinitrogen reduction. The reasons are explored and discussed. 相似文献
127.
128.
Xiaojuan Hao Luca Albertin L. John R. Foster Thomas P. Davis Christopher Barner‐Kowollik 《Macromolecular bioscience》2003,3(11):675-683
A novel synthetic method combining chemo and enzymatic synthesis strategies was employed to prepare a vinyl acetate type monomer, 6‐(4‐methoxybiphenyl‐4′‐oxy)hexyl vinyl hexanedioate (VA‐LC). Homo‐ and copolymers of VA‐LC with maleic anhydride (MAn) were prepared by conventional free radical polymerization using 2,2′‐azobisisobutyronitrile (AIBN) and 1,1′‐azobis (cyclohexane carbonitrile) (AHCN) as an initiator at 95 and 60 °C, respectively. The thermal properties of the generated polymeric material were investigated by differential scanning calorimetry (DSC), and the optical texture was inspected by polarizing optical microscopy (POM). While the monomer VA‐LC does not exhibit liquid‐crystalline properties, poly(VA‐LC), and the alternating copolymer of VA‐LC with maleic anhydride both displayed such properties.
129.
Joseph T. Klein Larry Davis Richard C. Effland 《Journal of heterocyclic chemistry》1987,24(3):725-731
The synthesis of a novel 2′,3′-dihydrospiro(benzofuran-2(3H),4′(1′H)isoquinoline] ring system ( IV ) by a nucleophilic aromatic fluoride displacement-cyclization is described. Preparation of various derivatives of IV as well as the precursor 4-(2-fluorobenzyl)-1,2,3,4-tetrahydro-4-isoquinolinols is also described. 相似文献
130.
M. T. Davis D. C. Stahl T. D. Lee 《Journal of the American Society for Mass Spectrometry》1995,6(7):571-577
A solvent delivery system is described that is designed to increase the efficiency of liquid chromatography-mass spectrometry (LC/MS) analyses. Gradients formed by using two low pressure syringe pumps are stored in a length of narrow bore tubing (gradient loop) mounted on a standard high pressure switching valve. The preformed gradient is pushed through the column by using a high pressure syringe pump. The system is fully automated and can be controlled with either a personal computer or the mass spectrometer data system. Advantages include gradient operation without the use of split flows, pressure programed flow control for rapid sample loading and recycling to initial conditions, and a flow rate range of 0.1–20 μL/min, which is suitable for packed capillary columns 50–500 μm in diameter. The system has been used extensively for rapid molecular weight determinations of intact protein samples, as well as LC/MS and liquid chromatography-tandem mass spectrometry analyses of complex peptide mixtures. 相似文献